Process for removing moisture from optical instruments



H. URQUHART Nov. 4, 19:47.

PROCESS FOR REIMOV ING MOISTURE FROM OPTICAL INSTRUMENTS Filed Sept. 14, 1944 IN VEN TOR. Hf/VEY 0,900/7 419 T ATTORNEY Patented Nov. 4, 1947 PROCESS FOR REMOVING MOISTURE FROM OPTICAL INSTRUMENTS Henry Urquhart, Buffalo, N. Y., assignor, by mesne assignments, to American Optical Company, Southbridge, Mass, a voluntary association Application September 14, 1944, Serial No. 554,112

1 Claim. 1

This invention relates to a new and improved process and apparatus for drying out or removing moisture from instruments.

An object of the invention is to provide a new and improved process and apparatus for drying out or removing residual moisture from the interior of an instrument,

Another object of the invention is to provide a new and improved process and apparatus for reducing the relative humidity of the gas employed in drying out an instrument for increasing the drying effect of such gases.

Other objects and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings. It will be understood that many changes may be made in the details of construction of the apparatus employed without departing from the spirit of the invention. I, therefore, do not wish to be limited to the exact details of construction of such apparatus as the form shown and described has been given by way of illustration only.

Referring to the drawings:

Fig. 1 is a perspective view of one form of apparatus which may be employed in carrying out the invention.

Fig. 2 is a sectional view taken on line 22 of Fig. 1 looking in the direction of the arrows.

Fig. 3 is a sectional view taken on line 33 of Fig. 2 looking in the direction of the arrows.

For several years past it has been the practice to dry out or remove residual moisture from the interior of an optical instrument to prevent any such moisture from condensing on the optica1 surfaces with a change in temperature and causing fogging of such optical surfaces and thereby interferes with the optical performance of the instrument.

The methods employed in the past have removed some of the residual moisture from the instrument but have not removed or reduced it to such an extent as to eliminate the possibility of such moisture condensing on the optical surfaces as stated above.

The method and apparatus of the present invention have been found to be much more eiTective and to practically insure the removal of such moisture to such an extent that the danger of any such fogging of the optical surfaces is substantially reduced or practically eliminated.

It, therefore, is the prime object of this invention to provide a new and improved process and apparatus for reducing or removing the residual moisture from the interior of an instrument to such an extent that the possibility of fogging of the optical surfaces thereof from this cause has been substantially eliminated.

Referring more particularly to the drawings wherein similar reference characters designate corresponding parts throughout the several views, the form of apparatus shown for carrying out the invention comprises a casing I which may be provided with a lining 2 of asbestos or other suitable insulating material. The casing I may be provided with a cover or if desired and the heating units are of suflicient capacity instead of a cover a screen or the like may be placed over the upper side of the casing I.

Extending through a wall of the casing I is the pipe or gas inlet 3 which connects a tank or the like (not shown) containing a suitable gas with the coil 4 having the portion 5 connected to the manifold 6 which may be secured to the inner side wall of the casing by brackets or the like'l.

The manifold 6 has the gas outlets 8 extending through the wall of the casing and to each of which is connected a hose or the like 9 having a connection at the outer end thereof having a threaded portion I9 adapted to engage a threaded portion in the instrument to retain the connection between the hose 9 and the instrument during the insertion of the gas into the instrument and to which a threaded cap I 0 may be secured in threaded engagement when the hose is not in use to prevent escape of the gas.

The coil 4 may if desired be supported within the casing I by the bracket II or other suitable supporting means such as a shelf or the like.

The casing I also is provided with the thermostat l2 adapted to receive electric current through the supply line I3 and this thermostat I2 has leads connecting the same with the bar members I4 each of which contains an electrical heating element for heating the gas within the coils 4, the heating element and electric connections thereto being electrically insulated from the bar member.

The bars I4 may be of any desired number for example three as shown in Fig. 1 and may be secured to the coils 4 by the fastening means I5 or other suitable means.

Each of the bars I4 and heating element supported thereby is connected to the thermostat [2 by means of the leads l6 and I I through which current is supplied to the heating element to cause said heating element to heat the gas within the coil 4.

The temperature to which the heating elements are raised and consequently the temperature to which the gas passing through the coil 4 is raised may be controlled by means of the thermostat 12 which automatically controls the temperature of the heating elements and thereby controls the temperature of the gas. The temperature of the heated gas is shown by a thermometer 18 having its bulb extending into one of the manifold outlets 8.

The gas employed is preferably a dry gas, that is, a gas from which a large part of the moisture has been removed such as dry nitrogen or other suitable gases.

The temperature to which the gas is heated should be as high as possible but must not be so high as to raise the temperature of the adhesive or cement which is employed for use in constructing the lens systems Of the optical instrument to its softening point which might disturb the optical characteristics of the lens system. For example, one cement which is frequently employed for this purpose has a softening point of approximately 125 F.

It has been found that the temperature of the gas should be maintained at a temperature substantially above room temperature, for example, approximately 25 F. above the room temperature, that is, above approximately 100 degrees and should be below atemperature which will interfere with the optical elements as stated above. For best results the temperature of the gas should be maintained as high as possible within this range in order to remove as much moisture as possible from the instrument without injuring the optical components thereof.

The time necessary to remove the moisture from the instrument depends upon several factors, namely, the temperature to which the gas is heated and the gas capacity of the instrument.

The instrument should be in a warmed state when the gas is applied so that the entry of the heated gas into the instrument will not substantially lower the temperature of the gas.

In removing the moisture from the instrument, which has a gas inlet and outlet, the heated gas as described above is supplied to the warmed instrument under pressure and allowed to pass therethrough as described above for a period of time sufficient to remove the moisture therefrom and then the instrument body is filled with heated gas under pressure, for example, from three to ten pounds and then sealed to retain this pressure in the body of the instrument.

From the foregoing it will be seen that I have provided simple, efficient and economical means and process for obtaining all of the objects and advantages of the invention.

Having described my invention, 1 claim:

The process for permanently ridding of moisture the interior of an optical instrument whose optics are assembled by a cement having a softening point of approximately F., said instrument having a gas inlet and a gas discharge outlet arranged for the flushing of gas through the interior of the instrument, which comprises preheating the instrument to adjacent 125 F., but slightly below the softening point of the cement, passing dehydrated gas through a heating conduit while imparting heat at a controlled rate to the walls of said conduit and maintaining said walls at a temperature such as to deliver the dehydrated gas from the conduit at a temperature adjacent 125 F. but slightly below said softening point, passing the dry hot gas from said conduit under pressure through said inlet to sweep out of the instrument any residuum of moist gas therein and continuing to flush the instrument until the interior thereof is rid of moisture, and sealing said inlet and outlet at the termination of said flushing process with the gas in said instrument maintained under a pressure of from three to ten pounds pressure.

HENRY URQUHART.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 526.201 Saulmann Sept. 18, 1894 1,402,021 Snelling Jan. 3, 1922 1,525,131 Hitchcock Feb. 3, 1925 1,539,846 Jansson June 2, 1925 1,553,745 Buck Sept. 15, 1925 1,846,158 Stickley Feb. 23, 1932 1,931,339 Zingone Oct. 17, 1933 2,125,372 Fox Aug. 2, 1938 2,138,164 Haven Nov. 29, 1938 2,148,885 Walter Feb. 28, 1939 2,213,395 Hopfield Sept. 3, 1940 2,228,588 Watson et al Dec. 3, 1940 2,237,569 Lofgren Apr. 8, 1941 2,257,394 Niersbach Sept. 30, 1941 FOREIGN PATENTS Number Country Date 560,000 Great Britain Mar. 15, 1944 

